Search

We obtained an order-of-magnitude estimate for the dispersion of light caused by the effect of quantum fluctuations on the propagation of electromagnetic waves in four-dimensional spacetime. We calculated the delay of the photons from cosmological gamma-ray bursts (GRBs) for the flat, open, and closed cosmological models. This delay is attributable to the effect of expansion of the Universe on the propagation of a dispersive light wave in space. Analysis shows that the delay of GRB photons contains a regular component related to the expansion of the Universe. We conclude that cosmological models of the Universe can be selected by the delay of emission of various energies from GRBs; the accuracy of measuring the parameter Δt/ΔE γ must be no lower than 10−6 s MeV−1.

We present the data on short-term variations of the intensity of secondary cosmic rays during thunderstorm periods. The effect is studied separately for the soft (electrons) and hard (muons) components of cosmic rays, their intensities being correlated with the near-earth electric field using a second-order polynomial. It is shown that the linear and quadratic terms are dominant for the soft and hard components, respectively. In addition, some irregular enhancements of the soft component just before lightning discharges are observed giving evidence in favor of some particle acceleration process. They can be considered as an experimental confirmation of the runaway breakdown theory developed for the process of lightning initiation.

The characteristics of hadrons with Eh > 50 MeV in EAS have been obtained. The measurements were per- formed at the CARPET-2 extensive air shower array. For showers with E0 > 6· 10 13 eV the duration of hadronic cas- cade in NM has been estimated. The dependence of the mean neutron multiplicity in the neutron monitor on the total num- ber of the change particles for EAS with Ne = 10 5 10 7 at a distance of 17 30 m from EAS axis has been measured. it is equipped with registration system which enables time in- tervals between pulses to be recorded with accuracy 1 µs. It allows studying such phenomenon as a neutron multiplicity, induced by hadrons of EAS.

The project of the Baksan Underground Scintil- lation Telescope (BUST) upgrade is presented. Additional outer layers of the detectors with fine spatial resolution will be mounted around BUST. Optimal dimensions of a counter, 0.125m◊ 0.125m◊ 0.03m were chosen with a simulation program. The functional diagram of BUSTs DAQ additional layers is presented. Modernization allows us to study the knee region using muon number spectrum measurements. BUST located underground at a depth of 850 m of wa- ter equivalent was designed to solve a number of physical problems which predetermined its construction and location (Alekseev et al., 1998). The telescope is a four-store building with dimensions of 16.7m◊ 16.7m◊ 11.1m and consists of four horizontal and four vertical planes. The total number of detectors is 3180. The analysis of the muon groups registered by BUST gives us an opportunity to obtain information about spectrum and composition of primary cosmic rays in the energy range of 1013 1016 eV (Petkov et al., 2008). The coordinates of fired detectors give the initial information for identification parameters of muon groups (arrival direction and number of muon tracks). In general, the number of muons cross- ing the telescope, n, and the number of the reconstructed muon tracks in a selected event, ntr, should not necessar- ily coincide with each other. When two or more muons are crossing BUST close enough to each other (comparable with the size of the detector), the number of reconstructed muon tracks will be less than the number of muons crossing BUST. Construction of additional external scintillation layers pro

High-precision measurements of the lateral distribution function (LDF) of charged particles near the axis of extensive air showers (EASes) were performed with the CARPET air shower array of the Baksan Neutrino Observatory for several ranges of Ne, including the knee region. For the sake of comparison with the experiment, calculations for primary protons and iron nuclei were made using the CORSIKA code (the QGSJET01C model of interaction). The measured experimental LDF is compared with our calculations.

We present the results from our search for gamma ray bursts of high energy with the Andyrchy air shower array of the Baksan Neutrino Observatory of the Russian Academy of Sciences’ Institute for Nuclear Research using experimental data for the period 1996–2006 (live time, 2290 days). These data were recorded by the array in the mode of detecting single-particle components of cosmic rays.

The energy spectrum of cosmic ray muons in the range of several TeV to PeV obtained through the analysis of multiple interactions of muons (the pair meter technique) in the Baksan Underground Scintillation Telescope (BUST) is presented. Results are compared with prior BUST data on the muon energy spectrum measurements and data of other experiments, along with calculations for different muon spectrum models.

A search for transient point sources of ultra-high-energy (UHE) γ-rays has been performed, based on the correlation of two extensive air shower arrays, BAKSAN (North Caucasus, 1700 m a.s.l., BAKSAN Neutrino Observatory, Russia) and EAS-TOP (Campo Imperatore, 2005 a.s.l., Laboratori Nazionali del Gran Sasso, Italy), which are located at very similar latitudes (φ≈43° N), and separated in longitude by Δλ≈33.7°. The search has been conducted at primary energy Eγ⩾5×1013 eV on the time scale of a daily source transit over the sky, observable in the northern hemisphere (19° The stability of the single detectors has been studied and verified up to high significance level. No coincident excess, not compatible with the expectations from statistical fluctuations, has been observed. The obtained upper limits to the rate of transient events, nγ, at 90% c.l., are • concerning the sky survey, in the declination band corresponding to the zenith, n γ /(Ωt) /(yr sr) with Φγ(Eγ>5×1013 eV)>2.0×10−11 cm −2 s−1 and duration Δt • concerning the candidate sources, e.g., for Markarian 421: nγ/t 5×1013 eV)>1.3×10−11 cm −2 s−1 and Δt A coincident episode from Markarian 421, observed on 15 January, 1994, with expected chance imitation rate nch= 0.01 is discussed.

Analysis of the experimental data for a long period of Baksan underground scintillation telescope (BUST) operation to search for very-high-energy muons is presented. The phenomenological parameters and the sensitivity of the method of multiple interactions, based on the concepts of the pair-meter technique, are discussed. The experimental distributions are compared with the results of calculations for a “conventional” muon spectrum, based on 3D simulation of muon passage through the telescope.

The method of separating muons and hadrons recorded by the Muon Detector of the Carpet-2 air shower array of Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences) is described. The results of studying characteristics of the muon and hadron components of extensive air showers (EAS) with Ne ≥ 105 are presented. For the range of distances 40–55 m from shower axes the numbers of hadrons with energies higher than 30 GeV and muons with energies above 1 GeV are obtained as functions of the shower size Ne.

Cosmic gamma-ray bursts with primary-photon energies ≥ 10 GeV are sought in the data from the Andyrchy array obtained in the mode of detection of a single cosmic-ray component during a net observation period of 2005.4 d. The distribution of fluctuations of the detector count rate agrees with the expected cosmic-ray background, the only exception being an event with a deviation of 7.9σ. Constraints on the number density of evaporating primordial black holes in a local region of the Galaxy are obtained for the chromospheric evaporation models.

The design of the fine grained 300 t liquid argon calorimeter BARS is described. The BARS electronics include about 30 K channels of low noise amplifiers and ADCs. The DAQ system makes it possible to select channels with signals above the chosen threshold. 48 scintillation hodoscopes placed inside the liquid argon are used to form the first level trigger. The total number of scintillation counters in liquid argon is 384. Sums of ionization signals are used to produce the second level trigger. Results of the first use of liquid argon calorimetry for the measurements of tagged neutrino interactions, cosmic-ray muon spectra and composition of extensive atmospheric showers are discussed.

The state of the art and the project of modernization of the extensive-air-shower array Carpet-2 of the Baksan Neutrino Observatory of the Institute for Nuclear Research, Russian Academy of Sciences are described. The modernized array will allow the performance of detailed study of variations in the cosmic ray intensity, the energy spectra and composition of primary cosmic rays in the energy range 1013–1016 eV, and the anisotropy of primary cosmic rays with energies above 1013 eV.

Fluctuations of the multiplicity in muon bundles is another characteristic of these bundles and can provide additional information both about the spectrum and composition of primary cosmic rays and about the model of their interaction. In this paper, the possibility of studying these fluctuations using the data of the Baksan underground scintillation telescope is considered.

Knee formation in the EAS size spectrum as a possible result of some portion of EAS's energy carried away by some missing EAS component is discussed. To explain the absence of the bump in calculated EAS size spectrum for the standard EAS development in the present day experiments, the model of "catastrophic" EAS development was proposed. The hypothesis that all the energy lost for the further shower development ELT finally passes into neutrino (¾ELT) and muons (¼ELT) is shown to be practically excluded by present experimental data.

EMMA (Experiment with MultiMuon Array) is a new approach to study the composition of cosmic rays at the knee region (1 − 10 PeV). The array will measure the multiplicity and lateral distribution of the high-energy muon component of an air shower and its arrival direction on an event-by-event basis. The array operates in the Pyh¨asalmi Mine, Finland, at a depth of 75 metres (or 210 m.w.e) corresponding to the cut-off energy of approximately 50 GeV for vertical muons. The data recording with a partial array has started and preliminary results of the first test runs are presented. nonPeerReviewed

A possible explanation of the “knee” in the cosmic ray spectrum by the change in hadron-hadron interactions at the corresponding energy is discussed. It is shown that, at c.m. energies above 5 TeV, the total proton-proton cross sections obtained from cosmic ray experiments exceed the asymptotic fit made over the collider data. Such a rise of the cross sections favors the hypothesis about new chromodynamically charged degrees of freedom, the threshold of their creation being about \(\sqrt {^\mathcal{S} knee} \approx 2.3 TeV\). The properties of these new particles which are needed are discussed.

A search for transient point sources of ultra-high-energy (UHE) gamma-rays has been performed, based on the correlation of two extensive air shower arrays, BAKSAN (North Caucasus, 1700 m a.s.l., BAKSAN Neutrino Observatory, Russia) and EAS-TOP (Campo Imperatore, 2005 a.s.l., Laboratori Nazionali del Gran Sasso, Italy), which are located at very similar latitudes (phi approximate to 43 degrees N), and separated in longitude by Delta lambda approximate to 33.7 degrees. The search has been conducted at primary energy E (gamma) greater than or equal to 5 x 10(13) eV on the time scale of a daily source transit over the sky, observable in the northern hemisphere (19 degrees < delta < 69 degrees), and for three sources, namely the Crab Nebula, Markarian 421 and Markarian 501, observed at TeV energies by atmospheric Cherenkov detectors. The stability of the single detectors has been studied and verified up to high significance level. No coincident excess, not compatible with the expectations from statistical fluctuations, has been observed. The obtained upper limits to the rate of transient events, n gamma, at 90% c.l., are concerning the sky survey, in the declination band corresponding to the zenith, n gamma/(Omega t)< 12/(yr sr) with Phi(gamma),(E-gamma > 5 x 10(13) eV)> 2.0 x 10(-11) cm(-2)s(-1) and duration Delta t < 8 h; concerning the candidate sources, e.g., for Markarian 421: n gamma/t < 7.7/yr with Phi(gamma),(E-gamma, > 5 x 10(13) eV) > 1.3 x 10(11) cm(-2) s(-1) and Delta t < 7.5 h. cm A coincident episode from Markarian 421. observed on 15 January, 1994, with expected chance imitation rate n(ch) = 0.01 is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.

For the purpose to register gamma-ray burst (GRB) the single secondary particle counting rate of the EAS “Andyrchy” array was used. The EAS “Andyrchy” array has been operating since 1996, the study is performed by searching for short increases of counting rate. The results obtained in sky survey (10° ≤ δ ≤ 70°) for 1996 – 2000 years (1055.6 days of live time) are presented.

We report a search for high energy (1 GeV–1 TeV) radiation of the short gamma‐ray bursts. For this purpose the single particle counting rate of the “Andyrchy” air shower array has been used. The data were collected during 1996–2006 years with the total live time of 2290 days. We investigated 29 well localized short GRBs that occurred in the field of view of “Andyrchy” array. Using the epoch folding method around trigger time of the bursts the upper limits on the fluence of prompt and extended high‐energy radiation have been obtained. A supposed detection for extended high‐energy radiation with duration of 24 s is discussed.

Current status and results of the experiment on recording neutrino bursts are presented. The observation time (since 1980) is 22.6 years. The upper bound of collapse frequency in our Galaxy is 0.10 y i1 (90% CL).

Cosmic gamma-ray bursts with primary-photon energies > 10 GeV are sought in the data from the Andyrchy array obtained in the mode of detection of a single cosmic-ray component during a net observation period of 2005.4 d. The distribution of fluctuations of the detector counting rate agrees with the expected cosmic-ray background, the only exception being an event with a deviation of 7.9 sigma. Constraints on the number density of evaporating primordial black holes in a local region of the Galaxy are obtained for the chromospheric evaporation models.

Temporal and energy characteristics of the very-high-energy gamma-ray bursts from evaporating primordial black holes have been calculated by assuming that the photospheric and chromospheric effects are negligible. The technique of searching for such bursts on shower arrays is described. We show that the burst time profile and the array dead time should be taken into account to interpret experimental data. Based on data from the Andyrchy array of the Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences), we have obtained an upper limit on the number density of evaporating primordial black holes in a local region of space with a scale size of ~10^{-3} pc. Comparison with the results of previous experiments is made., Comment: 6 pages, 6 figures

The flux of high-energy muons (threshold energy, 220 GeV) as a function of atmospheric temperature is measured using data from the Baksan Underground Scintillation Telescope (BUST). The temperature was measured every 12 h by radiosonde at different levels of observations. The results from studying the correlation coefficient between the counting rate of muons and the temperature of the atmosphere at different altitudes are presented.

The effect of Forbush decreases was studied for a flux of high-energy muons with a threshold of 220 GeV detected by the Baksan Underground Scintillation Telescope (BUST) of the Institute for Nuclear Research, Russian Academy of Sciences.

Search for neutrino bursts from collapsing stars with the Baksan underground scintillation telescope has been carried out since 1980. In this study, the experimental data obtained during the period from 2001 to 2005 inclusive are analyzed. The upper limit of the mean frequency of collapses in the Galaxy over the entire period of observations (the total live time is 21.83 yr) was found to be 0.105 yr−1.

We present the investigation of the Correlation and Temperature Coefficients as a function of the altitude of the temperature measurements. The flux of high-energy muons (threshold energy 220 GeV) as a function of atmospheric temperature is measured using data from the Baksan Underground Scintillation Telescope (BUST). The minima of the Correlation and Temperature Coefficients as a function of the altitude correspond to atmosphere tropopause and maxima are related to troposphere and stratosphere. The magnitude of temperature variation corresponding to minimum is approximately a half of the magnitude corresponding to maxima. The values of the Correlation and Temperature Coefficients around of the minimum are approximately a half of the corresponding values around of the maxima. The approximate coincidence of the minimum and maxima in the Correlation and the Temperature coefficients leads to the conclusion that this is due to not the magnitude, but rather to the temporal behaviour of the temperature in the respective regions of the atmosphere.

The characteristics of the thermal neutrons flux have been measured near the EAS core at the Carpet-2 EAS array. The thermal neutron detectors were placed on the floor of the tunnel of the Muon Detector (MD) and showers with a core near the MD were selected. Thermal neutrons multiplicity spectrum has been obtained for these showers. Measurements of the lateral distribution function of thermal neutrons at distances of 1-16 m from the shower axis have been performed. The mean number of the recorded thermal neutrons as a function of the number of hadrons crossing the MD has been measured.